This invention relates to a steam turbine used for geothermal power generation and provided with a plurality of steam valve chambers. More particularly, this invention relates to such a steam turbine capable of carrying out a partial load drive.
A steam turbine's output is generally controlled by either the so-called speed-throttling process, which comprises controlling the simultaneous operation of a plurality of regulating valves attached to one steam valve chamber, or the so-called nozzle speed regulating process, which comprises gradually controlling the operation of a plurality of regulating valves one after another. The former process, which causes all the regulating valves to be opened or closed at the same time, minimizes the flow loss of steam, and it is consequently favorably accepted in the full load operation of a steam turbine. In contrast, the latter process, which causes the regulating valves to be opened or closed one after another, assures the effective application of steam energy, and it is consequently well adapted for the partial load drive of a turbine.
Recently from the standpoint of saving energy, geothermal turbines have come to be applied in an increasing number. Since it is demanded to save geothermal water or hot springs as much as possible, the aforementioned speed-throttling process fails to be favorably accepted. Where, therefore, the geothermal water is utilized, the nozzle speed-regulating process is also demanded to be so improved as to attain a desired result. The reason is that, where the nozzle speed-regulating process is adopted for a turbine driven by the geothermal water, solid particles contained in the geothermal water such as those of compounds of, for example, arsenic, hydrogen and sulfur tend to be accumulated in those of the steam valve chambers which are not put into operation at the time of a partial load drive of the turbine; and if this objectable condition should be allowed to stand, then steam streams will flow less smoothly, leading to an increased loss of the steam pressure and the erosion and corrosion of the steam vlave chambers by the above-mentioned solid particles of impurities entrained with the geothermal water.